1. Field of the Invention
This invention relates to a device ancillary to a magnetic resonance imaging (MRI) system and more particularly to a display device through which the physician may monitor bioelectrical and biophysical phenomena in a patient real-time while scanning the patient with an MRI system in an MRI booth.
2. Description of the Related Art
The magnetic resonance imaging system has been proposed as a device for visualizing axial, coronal and sagittal sections of a patient's body without exposing the patient to radiation. The principle of this system comprises applying an electric wave energy (RF pulses) to a human body located in a strong magnetic field to cause the atomic nuclei to resonate in the body to form an image. Thus, when such nuclei within the body placed in a homogeneous magnetic field absorb energy from electric waves of a given wavelength, they release back the energy once absorbed and accumulated. The MRI is a device which constructs an image based on the above effect. While the atomic nuclus is usually H.sup.1, it may also be .sup.13 C, .sup.19 F, .sup.23 Na, .sup.31 p or the like.
FIG. 4 is a schematic diagram showing the manner in which the MRI device is used, where a technician 43 and a physician 44 are constructing an MRI tomogram of a patient 42 under constant monitor of the patient's condition in an MRI booth 41.
The magnetic resonance imaging system comprises an MRI unit 45, which employs a superconductive magnet or electromagnet, and an MRI control 46 which displays a tomogram and other information under the control of the technician 43. In order that a reliable tomogram may be constructed, there must be provision for protecting the magnetic field in the MRI booth 41 against external perturbations. Therefore, the MRI booth 41 is meticulously protected with a magnetic shield.
In operating the magnetic resonance imaging system, the patient's physiological status must be fully monitored. Therefore, a display monitor 47 is disposed near the physician 44 so that the physician 44 may have ready access to the electrocardiogram and, where necessary, the pulse wave signals and blood pressure signal waves of the patient. In the system illustrated in FIG. 4, only electrodes 48 attached to the patient's limbs for the detection of myocardial action potentials and a preamplifier 49 for amplifying the outputs of said electrodes 48 are shown and the sphygmomanometer and other instruments are not shown.
The physician 44 evaluates the physiological status of the patient 42 according to the waveforms and other data on the display monitor 47 and instructs the technician 43 on the operation of the MRI control 46. Assuming that the patient has a heart disease, the electrocardiogram, blood pressure and pulse rate are constantly monitored and if any ECG abnormality is discovered, an instruction is given to immediately stop the operation of the MRI unit 45.
However, the system shown in FIG. 4, wherein the physiological condition of a patient is monitored in a separate room independent of the MRI booth, has various drawbacks. Thus, since the physician is monitoring the patient's condition on the display monitor 47 which is located in the separate room, he cannot rush to the patient in the event of onset of a sudden abnormality in the patient with the result that institution of a pertinent remedy is delayed. Moreover, even in the absence of such a sudden abnormality, the patient left alone in the isolated noisy MRI booth often experiences anxiety and fear. Therefore, if possible, it is most desirable that the physician is attendant close by the patient throughout the diagnostic procedure.
In order that the physician may attend the patient at all times during diagnosis, it is necessary that the patient's physiological status be monitored within the MRI booth. To do this, however, the following problems must be solved for bringing the monitor display into the MRI booth.
(1) If other instruments are unscrupulously brought into the MRI booth, the magnetic field within the booth will be disturbed by influences of such instruments to interfere with the construction of a reliable tomographic image. Thus, there must be no generation of electric and other noise from instruments installed near the patient and the MRI unit. If, for example, the display monitor 47 is installed in the MRI booth, the MRI unit will fail to output accurate image data and increase the risk of a wrong diagnosis.
(2) The cathode-ray tube of the display monitor 47 is directly subject to influences of the magnetic field. Therefore, if a display device utilizing a cathode-ray tube is installed in the MRI booth, the device will naturally fail to display true waveforms. Even if the display device is not a device having a cathode-ray tube, the strong magnetic field in the MRI booth may still interfere with the display waveforms.
FIG. 5 shows a normal ECG (a), an ECG (b) recorded in a patient who has a history of myocardial infarction which is still persistent and an ECG (c) recorded in a patient which has myocardial infarction as a present illness. FIG. 6 shows a standard intraarterial waveform (a) characterized by two peaks and a blood pressure waveform (b) recorded in a patent with aortic valve disease. As will been seen from FIGS. 5 and 6, the difference between the normal waveform and the abnormal waveform is subtle and, moreover, the abnormal waveform can be of several types. Therefore, to prevent a wrong diagnosis, it is necessary that the ECG signals and blood pressure signals derived from the patient be displayed with the greatest fidelity.
(3) The wall isolating the MRI booth from the MRI control room must be strictly shielded electrically and magnetically. Therefore, it is difficult to lead many conductors into the MRI room. For example, it is impossible to transmit the ECG and blood pressure signal outputs from the auxiliary terminals of the display monitor independently into the MRI booth. It might be contemplated to use a single conductor on a time sharing basis for the transmission of the plurality of signals but the pulse signal necessary for time-sharing of the conductor would adversely affect the constructed image. Therefore, such a schema would not be a pertinent solution. Furthermore, the wiring between the MRI booth and the MRI control room is routed through an electromagnetically shielded under-floor box along the walls of the respective rooms and may be as long as about 15 meters and in this respect, too, it is not a valid procedure to lead feeble ECG and other signals into the MRI booth.
Having been accomplished in view of the above problems, this invention has for its object to provide a display device by which ECG, blood pressure and other signals can be accurately monitored within the MRI booth and which does not exert adverse influences on the MRI device.